For many decades, the internal mixing of the hot core and the cold bypass flow has been a proven method to improve both, the efficiency and the noise characteristics of low- and medium-bypass engines. The temperature fields are thereby homogenized and the maximum temperature at the nozzle exit plane is reduced. Since the exit velocity of a nozzle is significantly influenced by the temperature, the thermal mixing also causes lower jet velocities. This in turn leads to a more efficient exploitation of the available energy and to a reduced noise emission, as the latter, according to Lighthill’s theory, scales with the eighth power of the jet velocity. The partial shielding of the mixing noise by the nozzle additionally lowers the radiated sound. Due to the limited mixing space, so called lobed mixers are widely employed to divert cold fluid to the core and hot to the bypass to enhance the thermal transport. In addition to an improved mixing, these devices cause losses. Therefore, a careful design is essential, in which flow- and increasingly acoustic-simulations play an important role. As the quality of a simulation-based optimization is largely dependent on the accuracy of the used models, the improvement of these models is a major issue in the development of
new propulsion systems. The iterative optimization process involves a large number of simulations, wherefore the efficiency of a method also plays a decisive role. For this reason, the assessment and improvement of efficient numerical methods for the aerothermodynamic and aeroacoustic study of mixed turbofan engines is the object of this work. On the part of the aerothermodynamics, the focus is on an improved prediction of the mixing behaviour in shear-layers with temperature gradients. Therefore, experiments of cold and hot free-jets, as well as a mixed engine are simulated using different turbulence- and heat-flux-closures. Additionally, the measurements from the literature are supplemented by time-resolved simulations. The Reynolds-stress-model shows, in particular in combination with the temperature-correction developed in the scope of this work, a higher potential for improvements in comparison with simpler two-equation-models. In the aeroacoustic study, two transient approaches are compared and assessed regarding their applicability in an industrial environment. The RANS-based method by the German Aerospace Center (DLR) shows considerable advantages for experimental jets with respect to efficiency and robustness when compared with scale-resolving simulations. However, for reliable applications on real engine
configurations further comparisons with appropriate measurements are necessary. «

For many decades, the internal mixing of the hot core and the cold bypass flow has been a proven method to improve both, the efficiency and the noise characteristics of low- and medium-bypass engines. The temperature fields are thereby homogenized and the maximum temperature at the nozzle exit plane is reduced. Since the exit velocity of a nozzle is significantly influenced by the temperature, the thermal mixing also causes lower jet velocities. This in turn leads to a more efficient exploitatio... »